1. Technical Field
The present invention relates to a method for producing vegetable oil fuel, and specifically to a method for producing vegetable oil fuel useful as low-pollution alternative fuel for diesel engine.
2. Background Art
Though a diesel engine has advantages over a gasoline engine in fuel efficiency and endurance, air pollutants such as CO2, NOX, SOX and DEP (diesel engine particles) are largely included in exhaust gas emitted from this diesel engine, so that development of low-pollution fuel as an alternative to light oil has been advanced.
On the other hand, new diesel engines of low-pollution type or DEP eliminators have also been developed. However, since about 500 ppm of sulfur is included in conventional light oil, there is a problem that a function of the new engines or the DEP eliminators is decreased, and development of low-pollution fuel in which sulfur is lowered to 50 ppm or less is desired.
Eventually, there is a limit to technical approaches of improvement in the engine itself or improvement in its peripheral device in order to promote a decrease in pollution of the diesel engine, so that it is considered that approaches from an aspect of fuel are promising.
Recently, studies on alternative light oil using vegetable oil have been advanced among development of low-pollution fuel in which sulfur is not included. Among the studies, “methyl esterified fuel” obtained by mixing methanol (or ethanol) and a catalyst (sodium hydroxide) into vegetable oil (vegetable waste oil) and heating and stirring them and advancing a transesterification reaction, etc. has received attention.
The inventors of the present application revealed that a reaction product such as ozonide obtained by directly performing ozone treatment of vegetable oil and fat had combustibility and showed preferred properties acting as the alternative light oil than the conventional methyl esterified fuel and further the reaction product could improve concentrations of CO2, SOX and NOX included in exhaust gas of the diesel engine to 50 to 30% or less of a conventional level as compared with conventional light oil commercially available as disclosed in U.S. Pat. No. 6,364,917 B1.
However, the existing methyl esterified fuel has problems that viscosity, the pour point and the flash point are high as compared with commercially available light oil and also the yield is low in a production step, so that it is difficult to adopt the methyl esterified fuel as alternative light oil fuel at the present point in time. This is probably mainly attributable to the direct use of long-chain fatty acid ester (fatty acid ester with high molecular weight) obtained by methyl esterification of vegetable oil. Because of this, generally, the methyl esterified fuel is used in blend with light oil or kerosene in Europe and America.
Also, in the conventional art disclosed in the patent of U.S. Pat. No. 6,363,917 B1, there was a technical problem that viscosity of the reaction product is still at a high level as compared with commercially available light oil.